From the Guidelines
The initial screening test for pheochromocytoma should be measurement of plasma free metanephrines or 24-hour urinary fractionated metanephrines and catecholamines, as these tumors secrete excess catecholamines 1. This approach is supported by the American Heart Association, which recommends the measurement of circulating catecholamine metabolites as the screening test of choice for pheochromocytoma/paraganglioma 1. The diagnostic work-up for pheochromocytoma typically involves:
- Biochemical tests:
- Plasma free metanephrines or 24-hour urinary fractionated metanephrines and catecholamines
- Measurement of catecholamine metabolites, such as normetanephrine and metanephrine
- Imaging studies:
- CT or MRI of the abdomen and pelvis to locate the tumor
- Functional imaging with MIBG (metaiodobenzylguanidine) scintigraphy or PET scans to confirm the diagnosis and identify metastases According to the most recent guidelines, the best screening test for pheochromocytoma is plasma free metanephrines, which carries a 99% sensitivity and an 89% specificity 1. It is essential to note that pheochromocytomas can cause life-threatening hypertensive crises if undiagnosed, especially during procedures or surgeries, highlighting the importance of accurate diagnosis and timely treatment 1. Genetic testing is also recommended for all patients with pheochromocytoma, as up to 40% have an inherited syndrome 1. The recent Endocrine Society guideline recommends starting with computed tomography, with magnetic resonance imaging as an alternative, and metaiodobenzylguanidine scanning to further evaluate suspected metastatic disease 1. In patients with a high risk of metastases, functional imaging to detect bone metastases may be considered 1. Overall, a comprehensive diagnostic approach is necessary to ensure accurate diagnosis and effective management of pheochromocytoma.
From the Research
Diagnostic Tests for Pheochromocytoma
The diagnosis of pheochromocytoma, a type of adrenal gland tumor, relies on biochemical tests to detect the presence of catecholamines produced by the tumor. The following are some of the diagnostic tests used:
- Plasma free metanephrines: Measurements of plasma free metanephrines, including normetanephrine and metanephrine, are considered a useful test for the diagnosis of pheochromocytoma 2, 3, 4, 5, 6.
- Urinary fractionated metanephrines: Urinary fractionated metanephrines are also used as a diagnostic test, with high sensitivity and specificity for pheochromocytoma detection 4, 5.
- Urinary catecholamines: Urinary catecholamines, including epinephrine and norepinephrine, can be used as a diagnostic test, but have lower sensitivity and specificity compared to plasma free metanephrines and urinary fractionated metanephrines 4, 6.
- (131)I-MIBG scan: The (131)I-MIBG scan is a functional imaging test that can be used to diagnose pheochromocytoma, especially in cases where biochemical tests are inconclusive 3.
Test Characteristics
The characteristics of these diagnostic tests are:
- Plasma free metanephrines: High sensitivity (99%) and specificity (89%) for pheochromocytoma detection 4.
- Urinary fractionated metanephrines: High sensitivity (97%) and specificity (69%) for pheochromocytoma detection 4.
- Urinary catecholamines: Lower sensitivity (86%) and specificity (88%) for pheochromocytoma detection 4.
- (131)I-MIBG scan: High accuracy (100%) for pheochromocytoma detection, but may not be available in all centers 3.
Preanalytical Factors
Preanalytical factors, such as drug interference, can affect the results of these diagnostic tests. For example, sulfasalazine can interfere with the measurement of urinary fractionated metanephrines, leading to false-positive results 5. Therefore, it is essential to consider these factors when interpreting the results of these tests.